1. Field of the Invention
The present invention relates to a fuel nozzle apparatus, a gas turbine, and a method of controlling the fuel nozzle apparatus, that are suitably used for an aircraft for example.
This application is based on Japanese Patent Application No. 2007-050016, the content of which is incorporated herein by reference.
2. Description of Related Art
Due to recent exhaust gas regulations, it is required also in a gas turbine or the like to suppress the concentration of NOx contained in the exhaust gas.
In order to meet this requirement, there have been proposed various techniques for suppressing NOx concentration in a gas turbine to be used in a plant (for example, refer to Japanese Unexamined Patent Application, Publication No. Hei 11-210492).
Lean combustion is one example of a method of suppressing the concentration of NOx contained in exhaust gas mentioned above. However, simply reducing the amount of fuel to be injected from a fuel nozzle into a combustor of a gas turbine causes unstable fuel combustion, and does not allow a predetermined ability of the gas turbine to be demonstrated.
Consequently, there has been carried out a staging in which fuel injection in some of the fuel nozzles among a plurality of fuel nozzles is stopped and fuel is injected from the remaining fuel nozzles, thereby realizing lean combustion and stable fuel combustion for the overall-gas turbine.
In general, a fuel nozzle is in contact with high-temperature and high-pressure gas (for example, compressed air) flowing therearound, and furthermore, it is exposed to a high level of radiation heat generated from combustion within the combustor.
A fuel nozzle from which fuel is injected is cooled down by the fuel flowing inside the fuel nozzle. Therefore, the temperature of the fuel nozzle itself does not rise much and continuous fuel injection is possible.
On the other hand, in a fuel nozzle where fuel injection from the fuel nozzle has been stopped, the flow of fuel that cools down the fuel nozzle stops. Therefore the temperature of the fuel nozzle itself rises. In the fuel used for a gas turbine, when the temperature of the fuel exceeds a predetermined temperature (for example, approximately 170° C.), a carbonization reaction starts to occur. Therefore, there is a possibility of carbonated fuel causing clogging (hereinafter, referred to as caulking) in the fuel nozzle.
Also at the time of soak back immediately after the gas turbine is stopped, that is, at the time when fuel injection from the fuel nozzle is stopped and heat of the combustor has been transmitted to the fuel nozzle, the above mentioned caulking is likely to occur in the fuel nozzle.
Conventionally, in order to prevent caulking, the gas turbine is stopped after carrying out an idle operation and the temperature of the gas turbine has been thereby reduced, or there is provided a fuel purging mechanism for removing fuel from the fuel nozzle.